1. The Field of the Invention
This invention relates to the production of purified water by reverse osmosis, and more particular, to the simultaneous production of multiple grades of purified water from a unitary reverse osmosis apparatus.
2. The Prior Art
Production of purified water from an impure water source by reverse osmosis is becoming widely known and used. A number of types of impure water may be treated, including sea water, brackish water, river water, municipal supply water, etc. Various types of purified water products may be obtained, including so called "bottled water" grade, which is a high quality purified water used for drinking and cooking, and often containing 300 or less ppm TDS; and lower quality types of purified water, which may contain as high as 500 to 1,000 ppm TDS for municipal supply, or even up to 2,000 or greater ppm TDS for agricultural, stock feeding and industrial purposes. Such products may be produced by individually providing suitable operating conditions such as operating pressure, feed water flow and other conditions, as well as suitable apparatus, including membrane type, for desired salt rejection. Such processes and apparatus have heretofore, however, been designed to produce a single grade of product such as, for example, potable water from sea water, or bottled water grade from municipal supply water. Separate reverse osmosis systems or apparatus can, of course, be designed and used for production of various grades of water products from an impure water source, but this involves considerable expense for providing and operating special and separate apparatus for each different product water type desired. Separate pressure containers housing semipermeable membrane cartridges of specific characteristics and operated at specific water flow and pressure would be required. It is, however, difficult and more expensive to produce a high quality product water such as of bottled water grade from a highly impure feed, such as sea water; and is wasteful if only a small amount of water of this purity is required.
Ordinary and accepted living habits have generated the need for a household water supply consisting of a small amount of high quality water, such as of bottled water grade, for drinking, ice making and cooking, and a larger amount of water of lower quality, adequate, for example, for washing, sanitary purposes and garden watering. Simultaneous production of these two types of water in roughly their required proportional amounts from a single or unitary apparatus would be very advantageous. Industrial water needs often also require different grades of water for specific purposes, and often the purer grade is needed in minor amount.